Process for the transesterification of keto ester with alcohol using polyaniline salts as catalyst

ABSTRACT

The present invention provides a process for transesterification of ketoester using polyaniline salt as catalyst, said process comprising reacting a keto ester with an alcohol in presence of a catalyst at a temperature range of 50 to 120° C. for a period in the range of 4 to 24 hours and separating the esters from the reaction mixture.

FIELD OF THE INVENTION

[0001] The present invention relates to a process for thetransesterification of keto esters with alcohols using polyaniline saltsas catalyst.

BACKGROUND AND PRIOR ART REFERENCES

[0002] Transesterification is a reaction between an ester and othercompound, characterized by an exchange of alkoxy groups or of acylgroups and resulting in the formation of a different ester. Three typesof transesterification are known (Kirk-Othmer Encyclopedia of ChemicalTechnology (Ed., Jacqueline I. Kroschwitz), 4^(th) Edition, Vol. 9, Page774 and references therein)

[0003] 1. Exchange of alcohol groups, commonly known as alcoholysis. Inthis process the compound with which an ester reacts is an alcohol.

R—COO—R¹+R²—OH→R—COO—R²+R¹—OH

[0004] 2. Exchange of acid groups, acidolysis. In this process thecompound with which an ester reacts is an acid

R—COO—R¹+R²—COOH→R—COOH+R²—COO—R¹

[0005] 3. ester - ester interchange. In this process an exchange takesplace between two esters

R—COO—R¹+R²—COO—R³→R—COO—R³+R²—COO—R¹

[0006] A normal method of transesterification is characterized byequilibrium between reactants and products. Generally, one of thereactants should be added in excess to move the reaction towards forwarddirection and obtain good yields.

[0007] Transesterification is more advantageous than the ester synthesisfrom carboxylic acid and alcohol, due to poor solubility of some acidsin organic solvents. Some esters, especially methyl and ethyl esters,are readily or commercially available and thus serve conveniently asstarting materials in transesterification.

[0008] Transesterification via alcoholysis plays a significant role inindustry as well as in laboratory and in analytical chemistry. Thereaction can be used to reduce the boiling point of esters by exchanginga long chain alcohol group with a short one e.g. methanol, in theanalysis of fats, oils and waxes. Transesterification is applicable inthe paint industry for curing alkyl resin. It plays an important role inpolymerization and in cosynthesis of ethylene glycol and dimethylcarbonate from ethylene carbonate and methanol.

[0009] β-Ketoesters represents an important class of organic buildingblocks and is used for efficient synthesis of a number of complexnatural products. β-Ketoesters are multicoupling reagents withelectrophilic and nucleophilic sites proven to be valuable tools in awide variety of molecular systems. These β-ketoesters are important byvirtue of their facile bond formation at all four carbon atoms thatfeature in their ease of transformation to chiral building blocks anduse in chain extension reactions. They are one of the basic buildingblocks in the total synthesis of sex pheromones like serricornine andother natural products like thiolactomycin, trichodiene, polyoximicacid, chokol, protaglandin PGF_(2α), ar-pseudotsugonoxide, syncarpicacid, diplodialide and podophyllotoxin.

[0010] Most of the methods of transesterification of ketoesters are notgeneral and are equilibrium driven reactions where usage of excess ofone of the reactants is mandatory to obtain good yields. Process fortransesterification of keto esters has been carried out by using variouscatalysts such as Lewis acids ( Holmquist et al. J Org Chem., 1989; 54:3258), Dimethylamino pyridine (Taber et al. J. Org. Chem., 1985; 50:3618), Iron (III) perchlorate (Kumar et al. Ind. J. Chem., 1993; 32B:292), Zeolites (Balaji et al. Tetrahedron 1998; 54: 13237), Distannoxane(Otera et al. J. Org. Chem. 1991; 56 (18): 5307), Natural kaoliniticclay (Ponde et al. J. Org. Chem. 1998; 63: 1058), Amberlyst-15 (Chavanet al. Synth. Commun. 2001; 31(2): 289), Mo-ZrO₂ solid acid (Reddy etal. Synth. Commun. 1999; 29 (7): 1235), Sodium perborate (Bandagar etal; Chemistry Letters, 2001; 894), Solid acid catalyst (Chavan et al.U.S. Pat. No. 6,376,701, 2002).

[0011] Esterification is one of the most fundamental and importantreactions in organic synthesis. Conventionally, the processes of makingesters can be classified into the following three main categories:

[0012] (a) Liquid-phase esterification reaction utilizing a liquidcatalyst: This type of processes utilize liquid phase acid, such assulfuric acid, phosphoric acid, or sulfonic acid, as catalysts.

[0013] (b) Liquid phase esterification reaction utilizing a solidcatalyst: This type of processes typically utilizes inorganic salts,cationic ion exchange resin and solid acid catalyst etc.

[0014] (c) Gas phase esterification reaction: This type of processesutilize a variety of catalysts such as heteropolyacids, liquid phaseacids carried by a solid carrier, and zeolite in a gas phase reaction.

[0015] One of the problems associated with the liquid-phaseesterification reaction using liquid-catalyst is that the acidiccatalysts of sulfuric acid or sulfonic acid can cause corrosion problemsto the reactor. These liquid acid catalysts are also discharged alongwith the reaction products, thus causing severe waste disposal andpollution problems. The drawbacks of using mineral acid as catalyst are:(i)Catalyst can not be reused, (ii) Disposal of acid is notenvironmentally safe and it is not economical, (iii) Low selectivity isfrequently observed, (iv) Corrosion of the reaction vessel and reactors,(v) Not easy to handle and (vi) High inventory of the catalyst.

[0016] The solid-catalyst liquid-phase esterification reaction, whichtypically utilizes a cationic ion exchange resin as catalyst,ameliorates the corrosion and waste disposal problems experienced withthe liquid-catalyst liquid-phase processes, and results in simplifiedseparation procedure required between the reaction product andcatalysts. However, cationic ion-exchange resins typically exhibitrelatively poor heat-resistance, and they often lose substantialactivity after being subject to heat. Once the catalytic activity of thecationic ion-exchange resins is reduced, it is difficult to beregenerated.

[0017] In the gas phase esterification reaction, the reaction conditionsare maintained so that all the reactants and products are in the gasphase. Typically, inorganic materials are utilized as catalysts whichtypically exhibit excellent heat resistance and can be easily separatedfrom the reaction products. However, the gas phase reaction necessitatesa relatively large reaction vessel, resulting in large capitalinvestment cost. Furthermore, if the gas phase esterification reactionis utilized to produce unsaturated carboxylic esters, the high reactiontemperature often causes undesired by-products of polymers or oligomersto be produced. In certain instances, the high reaction temperature hascaused the alcohol molecules to be dehydrated to become ethers. Theseside-reactions will tend to cause the reaction catalysts to lose theiractivity and result in operational difficulties.

OBJECTS OF THE INVENTION

[0018] The main object of the present invention is to provide a processfor the transesterification of keto esters with alcohols usingpolyaniline salts as catalysts, which obviates the drawbacks as detailedabove.

[0019] Another object of the invention is to provide an eco-friendlyprocess for the transesterfication of ketoester.

SUMMARY OF THE INVENTION

[0020] Accordingly, the present invention provides a process fortransesterification of ketoester using polyaniline salt as catalyst byreacting said keto ester with an alcohol in presence of a catalyst andseparating the esters from the reaction mixture.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Accordingly, the present invention provides a process fortransesterification of ketoester using polyaniline salt as catalyst,said process comprising reacting a keto ester with an alcohol inpresence of a catalyst at a temperature range of 50 to 120° C. for aperiod in the range of 4 to 24 hours and separating the esters from thereaction mixture.

[0022] One embodiment of the invention relates to a process, in whichthe alcohol used is selected from a group consisting of butanol,hexanol, octanol, decanol, dodecanol, behnyl alcohol, benzyl alcohol,cyclohexanol, 2-ethoxy ethanol, 2-butoxy ethanol, 3-butyne-1-ol, allylalcohol, and menthol.

[0023] Another embodiment of the invention, the catalyst used is apolyaniline salt selected from a group consisting ofpolyaniline-sulfuric acid, polyaniline-hydrochloric acid andpolyaniline-nitric acid system.

[0024] Still another embodiment, the preferred reaction temperature isin the range of 100 to 110° C.

[0025] Still another embodiment, the ketoester used is selected from agroup consisting of methyl acetoacetate, ethyl acetoacetate and phenylacetoacetate.

[0026] Yet another embodiment, the reaction is carried out for a periodof 20 to 24 hours.

[0027] Yet another embodiment, the catalyst amount used is in the rangeof 10 to 30 weight percent of ketoester

[0028] Still yet another embodiment provides a process, wherein theamount of alcohol used is 1.0 to 2.5 equivalent with respect to oneequivalent of keto ester.

[0029] Another embodiment of the invention, the catalyst used isrecycled.

[0030] These embodiments will be apparent from the ensuing detaileddescription of the present invention.

[0031] The process of transesterification may be carried out by reactingketo ester with alcohol in presence of catalyst, and then removing thecatalyst by conventional methods. The ester can be isolated by methodssuch as filtration followed by isolation of esters by conventionalcolumn chromatography or vacuum distillation.

[0032] The novelty of the invention lies in the use of polyaniline-saltsas catalysts in the liquid phase esterification of keto esters withalcohols for the first time. Also, the use of polyaniline salts ascatalysts provides the following advantages (i) separation of catalystfrom a reaction mixture is easy, (ii) repeated use of catalyst ispossible and (iii) there is no problem for the disposal of used catalystas they are environmentally safe.

[0033] The following examples are given by way of illustration andtherefore should not be construed as limit the scope of the presentinvention.

EXAMPLE 1

[0034] The following example illustrates the preparation of esters withdifferent reaction time.

[0035] In a typical experiment, one equivalent (1.0 g) of ethylacetoacetate was taken in 10 ml round bottom flask and added twoequivalent (1.5 g) of hexanol followed by 200 mg of polyaniline-sulfatesalt catalyst powder (20 wt % with respect to ethyl acetoacetate). Thereaction mixture was refluxed at 110° C. for different intervals oftime. The reaction mixture was filtered, washed with dichloromethanesolvent and the solvent was evaporated. The percentage conversion ofethyl acetoacetate was estimated by ¹H NMR spectra using Varian Gemini200 MHz spectrometer.

[0036] The percentage conversion ethyl acetoacetate with differentreaction time is given in Table 1. TABLE 1 REACTION TIME (hrs.)CONVERSION (%) 4 42 8 76 10 84 14 87 16 96 20 96 24 96

EXAMPLE 2

[0037] The following example illustrates the preparation of esters withdifferent amount of catalyst

[0038] In a typical equivalent (1.0 g) of ethyl acetoacetate was takenin 10 ml round bottom flask and added two equivalent (1.5 g) of hexanolfollowed by different amount of catalyst powder (polyaniline-sulfatesalt). The reaction mixture was refluxed at 110° C. for 24 hrs. Thereaction mixture was filtered, washed with dichloromethane solvent andthe solvent was evaporated. The percentage conversion of ethylacetoacetate was estimate by ¹H NMR spectra.

[0039] The percentage conversion of ethyl acetoacetate with differentamount of catalyst is given Table 2 TABLE 2 AMOUNT OF CATALYST (mg.)CONVERSION (%) 100 92 150 96 200 96 300 96

EXAMPLE 3

[0040] The following example illustrates the preparation of esters withdifferent amount of alcohol.

[0041] In a typical experiment, one equivalent (1.0 g) of ethylacetoacetate was taken in 10 ml round bottom flask and added differentequivalent of hexanol followed by 200 mg of polyaniline-sulfate saltcatalyst powder (20 wt % with respect to ethyl acetoacetate). Thereaction mixture was refluxed at 110° C. for 24 hrs. The reactionmixture was filtered, washed with dichloromethane solvent and thesolvent was evaporated. The percentage conversion of ethyl acetoacetatewas estimated by ¹H NMR spectra.

[0042] The percentage conversion of ethyl acetoacetate with differentamount of alcohol is given in Table 3. TABLE 3 Ethylacetoacetate:Hexanol(equivalent) CONVERSION (%) 1.0:1.0 67 1.0:1.2 77 1.0:1.5 90 1.0:2.0 96

EXAMPLE 4

[0043] The following example illustrates the preparation of esters withdifferent temperature.

[0044] In a typical experiment, one equivalent (1.0 g) of ethyl acetoacetate was taken in 10 ml round bottom flask and added two equivalent(1.5 g) of hexanol and 200 mg of catalyst powder (polyaniline-sulfatesalt). The reaction mixture was refluxed at different temperatures for24 hrs. The reaction mixture was filtered, washed with dichloromethanesolvent and the solvent was evaporated. The percentage conversion ofethyl acetoacetate was estimated by ¹H NMR spectra.

[0045] The percentage conversion of ethyl acetoacetate with differenttemperature is given in Table 4. TABLE 4 TEMPERATURE (° C.) CONVERSION(%) 90 51 110 96 120 85

EXAMPLE 5

[0046] The following example illustrates the preparation of esters withdifferent alcohol.

[0047] In a typical experiment, one equivalent (1.0 g) of ethylacetoacetate was taken in 10 ml round bottom flask and added twoequivalent of different alcohol and 200 mg of catalyst powder(polyaniline-sulfate salt). The reaction mixture was refluxed at 110° C.for 24 hrs. The reaction mixture was filtered, washed withdichloromethane solvent and the solvent was evaporated. The percentageconversion of ethyl acetoacetate was estimated by ¹H NMR spectra.

[0048] The percentage conversion of ethyl acetoacetate with differentalcohol is given in Table 5. TABLE 5 ALCOHOL CONVERSION (%) Butanol 94Hexanol 96 Octanol 94 Decanol 90 Dodecanol 92 Behnyl alcohol 94 Benzylalcohol 72 Cyclohexanol 85 2-ethoxy ethanol 96 2-butoxy ethanol 963-butyne-1-ol 90 Allyl alcohol 23 Menthol 94

EXAMPLE 6

[0049] The following example illustrates the preparation of esters withdifferent keto ester.

[0050] In a typical experiment, one equivalent (1.0 g) of keto ester wastaken in 10 ml round bottom flask and added two equivalent (1.5 g) ofhexanol and 200 mg of catalyst powder (polyaniline-sulfate salt). Thereaction mixture was refluxed at 110° C. for 24 hrs. The reactionmixture was filtered, washed with dichloromethane solvent and thesolvent was evaporated. The percentage conversion of ethyl acetoacetatewas estimated by ¹H NMR spectra.

[0051] The percentage conversion of ethyl acetoacetate with differentketo ester is given in Table 6. TABLE 6 KETO ESTER CONVERSION (%) Methylacetoacetate 96 Ethyl acetoacetate 96 Phenyl acetoacetate 90

EXAMPLE 7

[0052] The following example illustrates the preparation of esters usingthe recovered catalyst for three times.

[0053] In a typical experiment, one equivalent (1.0 g) of ethylacetoacetate was taken in 10 ml round bottom flask and added twoequivalent of decanol followed by 200 mg of polyaniline-sulfate saltcatalyst powder (20 wt % with respect to ethyl acetoacetate). Thereaction mixture was refluxed at 110° C. for 24 hrs. The reactionmixture was filtered, washed with dichloromethane solvent and thesolvent was evaporated. The percentage conversion of ethyl acetoacetatewas estimated by ¹H NMR spectra.

[0054] The experiment was carried out three times more using therecovered catalyst. The yield of the ester prepared with recoveredcatalyst is given in Table 8. TABLE 8 REPEATABILITY (no of times)CONVERSION (%) First 90 Second 88 Third 90

EXAMPLE 9

[0055] The following examples illustrate the preparation of esters withdifferent catalyst.

[0056] Polyaniline salts were prepared using ammonium persulfateoxidizing agent (Method I, See Palaniappan et al. Poly. Adv. Tech.,1994, 5: 225) and benzoyl peroxide oxidizing agent (Method II, SeePalaniappan et al. Green Chemistry, 2002; 4: 369).

[0057] In a typical experiment, one equivalent (1.0 g) of ethylacetoacetate was taken in 10 ml round bottom flask and added twoequivalent (1.5 g) of hexanol followed by 200 mg of differentpolyaniline salt (polyaniline-hydrochloride, polyaniline-sulfate,polyaniline-nitrate salt) catalyst powder (20 wt % with respect to ethylacetoacetate). The reaction mixture was refluxed at 110° C. for 24 hrs.The reaction mixture was filtered, washed with dichloromethane solventand the solvent was evaporated. The percentage conversion of ethylacetoacetate was estimated by ¹H NMR spectra.

[0058] The percentage conversion of ethyl aceto acetate with differentcatalyst is given in Table 9. TABLE 9 METHOD POLYANILINE SALT CONVERSION(%) I Polyaniline hydrochloric acid system 90 Polyaniline sulfuric acidsystem 96 Polyaniline nitric acid system 94 II Polyaniline hydrochloricacid system 91 Polyaniline sulfuric acid system 96 Polyaniline nitricacid system 94

Advantages of the Present Invention

[0059] The main advantages of the present invention are

[0060] a) Use of polyaniline-salts as catalysts in the liquid phaseesterification of keto esters with alcohols for the first time.

[0061] b) Also, the use of polyaniline salts as catalysts provides thefollowing advantages

[0062] (i) separation of catalyst from a reaction mixture is easy,

[0063] (ii) repeated use of catalyst is possible,

[0064] (iii) there is no problem for the disposal of used catalyst asthey are environmentally safe, though the disposal of mineral acidcatalyst requires much money for treatment to make it environmentallysafe, and

[0065] (iv) the preparation of the catalyst is straight forwardsynthetic route.

[0066] In view of the above, it can be seen that several advantages ofthe invention are achieved and other advantageous results attained. Asvarious changes could be made in the above methods and compositionswithout departing from the scope of the invention, it is intended thatall matter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

1. A process for transesterification of ketoester using polyaniline saltas catalyst, said process comprising reacting a keto ester with analcohol in presence of a catalyst at a temperature range of 50 to 120°C. for a period in the range of 4 to 24 hours and separating the estersfrom the reaction mixture.
 2. A process as claimed in claim 1, whereinthe alcohol used is selected from a group consisting of butanol,hexanol, octanol, decanol, dodecanol, behnyl alcohol, benzyl alcohol,cyclohexanol, 2-ethoxy ethanol, 2-butoxy ethanol, 3-butyne-1-ol, allylalcohol, and menthol.
 3. A process as claimed in claim 1, wherein thecatalyst used is a polyaniline salt selected from a group consisting ofpolyaniline-sulfuric acid, polyaniline-hydrochloric acid andpolyaniline-nitric acid system.
 4. A process as claimed in claim 1,wherein the reaction is carried out preferably at a temperature range of100 to 110° C.
 5. A process as claimed in claim 1, wherein the ketoesterused is selected from a group consisting of methyl acetoacetate, ethylacetoacetate and phenyl acetoacetate.
 6. A process as claimed in claim1, wherein the reaction is carried out for a period of 20 to 24 hours.7. A process as claimed in claim 1, wherein the catalyst amount used isin the range of 10 to 30 weight percent of ketoester.
 8. A process asclaimed in claim 1, wherein the amount of alcohol used is 1.0 to 2.5equivalent with respect to one equivalent of keto ester.
 9. A process asclaimed in claim 1, wherein the catalyst used is recyclable.